1. Field of the Invention
This invention relates to an excellent adhesive primer composition. More specifically, this invention relates to a primer composition which is appropriate for attaching thermosetting-type silicone rubber, especially fluorosilicone rubber, to various materials, such as metal surfaces. This invention also relates to a method of bonding a thermosetting silicone rubber to a substrate.
2. Description of the Prior Art
It is a known fact that vinyltris(tertiary-butylperoxy)silane is traditionally used as a primer for attaching EPDM, EPR, chlorinated polyethylene or silicone rubber or glass or metal surfaces. However, this primer exhibits drawbacks such as the necessity of long-term heat treatment at an elevated temperature and pressure. For this reason, Maizumi and Inoue in Japanese Patent No. Sho 50[1975]-35,530, published Nov. 17, 1975, describes an adhesive primer composition which can be used as a primer for attaching thermoplastic resins to each other or attaching thermoplastic resin to glass, metals or metal oxides at low temperatures in a short period of time. The primer composition of Maizumi and Inoue is composed of vinyltris(tertiary-butylperoxy)silane, an organoperoxide whose half-life is 1 minute at 130.degree.-190.degree. C., and an inert organic solvent. However, this primer composition of Maizumi and Inoue exhibits slow air-drying and slow thermosetting properties after it has been coated over with a material to be attached. Therefore, the primer layer coated on the material surface moves from one location to another location by press insertion of material during injection- or press-molding processes. For this reason, this primer composition of Maizumi and Inoue exhibits not only drawbacks such as difficulty in achieving uniform adhesion, but also the drawback of interfacial delamination which can be detected by inspection of the adhesion properties of silicone rubber, especially fluorosilicone rubber as a material to be attached. For this reason, this primer composition of Maizumi and Inoue is unsatisfactory for attaching silicone rubber to a substrate, especially for attaching fluorosilicone rubber to a substrate.